1. Field of the Invention
The present invention relates to a camera having a subject tracking function that can automatically track a subject that is moving within a subject field. More particularly, the present invention relates to a camera and a method that can quickly modify a tracking subject without changing the framing.
2. Description of the Related Art
Laid open patent number Sho 60-249477, entitled Automatic Tracking Focal Point Detection Device, teaches a device which automatically tracks a moving object, detects a focal point and adjusts the focal point. This is illustrated in prior art FIG. 1.
The tracking device forms an image of subject light that passes through a photographic lens 20 onto an image pick up element 21 composed of a charge-coupled device (CCD). The image pick up element 21 outputs a series of electric signals that have undergone photoelectric conversion. The output signals are input to a signal processing circuit 22 which converts them to, for example, National Television Standards Committee (NTSC) video signals which are then output.
At the same time, color differentiated signals are output from the signal processing circuit 22. The color data is extracted as a characteristic of the targeted subject by a color detection circuit 23. This data is placed in memory in a tracking unit 24. Tracking unit 24 compares this memorized color information with newly extracted color information for every field, and, based on the results of this comparison, determines the presence or absence of subject movement. When the targeted subject moves, the targeted subject is automatically tracked by moving the distance measurement visual field to track that movement, detecting the focal point, and adjusting the focal point.
A detailed explanation of how the movement of the targeted subject is determined by color information is omitted here. However, three contiguous pixels are set up as the visual field to be tracked. Tracking is conducted based on the changes in position on a coordinate system made when plotting the color differentiated signals of each pixel (R-Y), (B-Y) on the orthogonal coordinates (R-Y), (B-Y), where R is red, Y is yellow and B is blue.
In this regard, the tracking unit in the conventional technology described above operates well when tracking the target subject accurately according to the intention of the photographer. However, a reset action, such as correcting the framing so that the targeted subject to be tracked is in the center of the subject field, must be done every time the targeted subject deviates from the intention of the photographer or every time the targeted subject being tracked changes to another subject within the same frame. This has the disadvantage that picture taking opportunities are missed.